The present invention relates to a data storage device, and more particularly to a data storage device suitable for a hard disk drive.
As a data storage device, various devices each using a medium are known—there are various kinds of media such as an optical disk and a magnetic tape. Among them, a hard disk drive has achieved widespread use as a storage device of a computer, serving as one of the indispensable storage devices for current computer systems. In addition, the superior characteristics of the hard disk drive are more and more widening the use of the hard disk drive; more specifically, the hard disk drive is applied not only to the computer systems, but also to, for example, a moving image recorder/player, a car navigation system, and a removable memory used for a digital camera, etc.
The hard disk drive comprises the following components: a magnetic disk for storing data; a head for reading/writing data from/to the magnetic disk; and an actuator for moving the head to a desired position on the magnetic disk. When a voice coil motor drives the actuator, the actuator pivotally moves about a pivot, which causes the head to move in the radial direction on the magnetic disk that is rotating. This permits the head to access a desired track formed on the magnetic disk, and thereby to read/write data.
The actuator includes a suspension with elasticity, and the head is firmly fixed to the suspension. The head includes a write/read thin film element and a slider. By balancing the pressure produced by air viscosity between the rotating magnetic disk and an ABS (Air Bearing Surface) surface of the slider, which faces the magnetic disk, against the pressure applied by the actuator in a direction toward the magnetic disk, the magnetic head floats off the magnetic disk with a constant gap being kept.
The spindle motor secured to the base rotates the magnetic disk at a given speed. FIG. 7 is a cross-sectional view partially illustrating how a spindle motor 701 used for the conventional hard disk drive and the base 702 for receiving the spindle motor are configured. The spindle motor 701 is a fluid dynamic bearing motor in which oil is used for a bearing. From the standpoint of its silent operation, the durability, and the like, instead of the ball bearing motor, the fluid dynamic bearing motor is more and more adopted for the hard disk drives. In FIG. 7, the spindle motor 701 has an axial rotation structure in which a rotating shaft (shaft) is secured to the rotating hub side. The base 702 is formed by casting aluminum alloy. In addition, with the object of achieving a desired shape with required accuracy, a part of the base 702 is formed by cutting. It is to be noted that one example of the fluid dynamic bearing motor is disclosed in Japanese Patent Laid-Open No. 2003-143803, for example.
In FIG. 7, reference numeral 703 denotes a hub to which a magnetic disk is secured. In an example shown in FIG. 7, the hub 703 is formed of magnetic metal such as SUS. Reference numeral 704 denotes a rotating shaft. The shaft 704 is secured to the center of the inner surface of the hub 703. Reference numeral 705 denotes a rotor magnet. The rotor magnet 705 has a cylindrical shape, and is firmly fixed to the inner surface of the hub 703. The hub 703, the shaft 704, and the rotor magnet 705 constitute a rotor 706 that is formed as one unit. Reference numeral 707 is a sleeve for accommodating the shaft 704.
The sleeve 707 is provided with a bearing hole 707a for accommodating the shaft 704. The shaft 704 is rotatably accommodated in the bearing hole 707a. On the inner surface of the bearing hole 707a, there is formed a radial dynamic pressure groove for producing dynamic pressure. Oil is applied between the shaft 704 and the inner surface of the bearing hole 707a, which allows to serve as a radial bearing 708. On the top surface of the sleeve 707 that is in contact with the inner surface of the hub 703, there is formed a thrust dynamic pressure groove for producing dynamic pressure. Oil is applied between the top surface of the sleeve 707 and the inner surface of the hub 703, which allows to serve as a thrust bearing 709.
Reference numeral 710 denotes a stator coil for applying an electric current to the spindle motor. Reference numeral 711 denotes a stator core. The stator coil 710 is wound around the stator core 711. The stator core 711 is placed inside the rotor magnet 705 so that the stator core 711 faces the rotor magnet 705. The stator coil 710 and the stator core 711 constitute the stator 712 that is formed as one unit.
When the stator coil 710 is energized, the rotating magnetic field generated by the stator 712 produces torque, and consequently the rotor 706 starts rotating. In response to the rotation of the rotor 706, a plurality of radial dynamic pressure grooves formed on the inner surface of the bearing hole 707a create pressure on the radial bearing 708. In a similar manner, the plurality of thrust dynamic pressure grooves formed on the top surface of the sleeve 707, which is in contact with the inner surface of the hub, create pressure on the thrust bearing 709, and thereby the hub 703 floats off the top surface of the sleeve 707. As a result, the rotor 706 can rotate in a non-contact state.
As for the spindle motor 701, the thrust bearing 709 in a direction of the rotating shaft (vertical direction in FIG. 7) is formed only between the top surface of the sleeve 707 and the inner surface of the hub 703. For this reason, the buoyant force is applied to the rotor 706 in the upward direction (in a direction from the base 702 toward the hub 703). For the purpose of forming the magnetic back pressure that balances against this buoyant force, a bias plate 713 made of a magnetic material is firmly fixed to the bottom of the base 702. By use of the magnetic back pressure produced between the rotor magnet 705 and the bias plate 713, it is possible to attract the rotor 706 toward the base 702 against the buoyant force by the thrust bearing 709, and thereby to control the rotation of the rotor 706.
In the conventional hard disk drive described above, forming the thrust bearing 709 only on one side in the direction of the rotating shaft renders it possible to make the hard disk drive thin. However, because the base 702 is formed of non-magnetic material aluminum alloy, the bias plate 713 for controlling the floating of the hub 703 in the thrust bearing 709 needs to be formed separately from the base 702.
In another case, the base 702 in the conventional hard disk drive is formed by casting. Because the floating of the hub is determined by a gap between the bias plate 713 and the rotor magnet 705, a mounting surface of the bias plate 713 on the base 702 is required to be formed with a higher degree of accuracy. Accordingly, a fixing area of the base 702, to which the bias plate 713 is fixed, is required to be formed by cutting after casting, which makes the manufacturing process more and more complicated.